A disk array device comprises a cache memory for temporarily storing data. When there is a write access from a host computer to a disk drive, the completion of write processing is notified to the host computer when the write data is written into the cache memory. When there is a read access from the host computer to the disk drive, high-speed access is realized by reading data from the cache memory if the read data is a cache hit.
However, since many of the cache memories are configured from a volatile memory, there are cases where the cache data is lost if the power supply to the cache memory is suspended due to a power source failure or the like.
In light of the above, there are disk array devices equipped with a large capacity battery. With this type of disk array device, since electric power can be supplied from the large capacity battery to the cache memory and the like, the business operation can be continued without being suspended even during a power failure as a result of feeding power from the large capacity battery to the cache memory from the time of power failure to the time of power restoration.
Nevertheless, if a large capacity battery is mounted, the disk array device will become expensive since the large battery is costly. In addition, even upon using a large capacity battery, there is a battery capacity is limited, there will be no choice but to suspend the business operation if the length of the power failure is prolonged.
Meanwhile, if a small battery of a small capacity is mounted on the disk array device in substitute for the large capacity battery, increase in costs as a result of mounting a battery can be suppressed. Here, a system may be considered of saving data stored in a volatile memory to a nonvolatile memory during a power failure, feeding power to the volatile memory from the battery during power restoration, returning the data stored in the nonvolatile memory to the volatile memory, and resuming the business operation based on the data that was returned to the volatile memory.
In the foregoing case, as described in Patent Literature 1, it is also possible to adopt a system of increasing the amount of data to be written into the memory and also increasing the amount of data to be read, and increasing the storage capacity of each recording operation of the optomagnetic disk when the remaining battery level is high, and reducing the amount of data to be read from the memory and reducing the storage capacity of each recording operation of the optomagnetic disk if the battery capacity is low. Moreover, as described in Patent Literature 2, it is also possible to adopt a system of selecting the operation mode of the storage system according to the battery capacity during a power source failure.